The present invention relates generally to steam turbines, and more particularly, to operating a steam turbine reheat section of a steam turbine with an overload valve.
Steam turbines, especially those that are associated with combined-cycle power plants, can operate under various operating conditions. For example, heat recovery steam generator (HRSG) supplemental firing is often used with steam turbines in combined-cycle power plants to enable the plant to respond to fluctuations in load demand. Typically, this can be helpful in improving peak power production or enabling higher steam production to compensate for the lack of production from another unit within the plant. Generally, supplemental firing results in more steam being supplied to the steam turbine. Typically, this increase in steam flow, as a result of supplemental firing, results in an increase of steam flow to the high pressure turbine section, which will cause an increase of flow of steam supplied to the remaining lower pressure turbine sections. This increase in steam flow results in increased pressures at the steam admission inlets of these lower pressure turbine sections. An increase in pressure at the steam admission inlets of these lower pressure turbine sections has implications on the components used in these sections. For example, the components of these lower pressure turbine sections typically have to be designed to withstand substantial increases in pressures that can arise due to supplemental firing. Designing these lower pressure turbine sections to withstand substantial increases in pressures that can arise during supplemental firing can be costly and add complexity to the overall operation of the power plant.